The situation is complex - people don't just decide to not have sex anymore. What is comes down to, says Anita Rani, is that in a society which is still quite conservative and traditional, women who have children only have one option: to quit their jobs and not return to the workforce.

Japanese women may have been content to do that in the past, but they certainly aren't anymore. "Children are one of the many reasons they aren’t having sex or forming relationships," she says. "Only 2% of couples in Japan have kids out of wedlock – in Britain, that figure is nearly 50%.

"We forget that it’s an Asian country so they are conservative even though it’s really modern. You’re completely blown away at how high tech it is when you arrive there. But when you scratch beneath the surface, it is traditional and women are expected to be housewives and bring up the kids. There is no place in the workforce for them after they have children and that is a big problem. This generation now has opted out of having sex – it’s a strange thing that can only happen in Japan."

The key problem is that women and men are growing into two very different types of human beings. The women that Anita met, she says, "are massively assertive" and are outperforming men. But while they are forging ahead, the men are retreating into themselves and aren't taking the reins. "They're emasculated," adds Anita, "but that's their own doing."

While she was out there, Anita met two Otaku men- which refers to a group of people obsessed with Manga and video games. Both had virtual girlfriends and one of the men is actually married to a proper human being. These two are in their late 30s, and Anita says, have completely rebelled against the traditional image of a Japanese salary-man who'd work all hours for the company.

"The traditional work ethic is what re-built Japan post-war, but now its biting the country on its arse. It has now been economically stagnant for 20 years – this generation has seen their parents work so hard and have thought: that’s not the life for me. These two Otaku guys were deadly serious – when I asked the married guy who he would pick the wife or the virtual girlfriend – he actually paused to think."

So what does she advise for the future? "Immigration is an issue they won't discuss," she says, "and there are going to be serious consequences if they don't change the way their workforce is structured. At the moment, women who do have children don't want to return because they are worried about inconveniencing their colleagues - can you imagine that? They don't want to make their colleagues pick up the slack when they have to look after their children.

"But something must be done. The elderly are not dying and they won't have any young people to look after them soon, and there will be even fewer people who have jobs who will be paying taxes."